Technical Field
The present invention relates to a lighting apparatus, and an image projection apparatus.
Background Art
Image projection apparatuses known as projectors have been widely used for presentations, meetings, signage with the advancement of higher resolution of liquid crystal panels, enhancement of brightness of lamps having increased efficiency, and lower price.
Further, light-weight and compact image projection apparatuses employing digital light processing (DLP) using digital micro-mirror devices (DMD) as an image generation element have been widely used in offices, schools, and homes. Further, image projection apparatuses of short focus distance are developed. Further, the image projection apparatuses can employ various lamps as the light source such as an arc lamp (e.g., high pressure mercury lamp, xenon lamp).
As to an optical lighting system of the DLP image projection apparatus such as a lighting apparatus, a light tunnel having inner faces formed as mirror faces can be used as a light equalizer. Specifically, light emitted from the lamp is separated into a plurality of colors, and then guided into the inner faces of the light tunnel. The light is reflected on the inner faces in the light tunnel for a plurality of times, and then the light exits to the image generation element via a lens and a mirror to focus the light on the image generation element. In this configuration, the light axis of the light emitted from the lamp and guided to the light tunnel is aligned to the center axis of the light tunnel, or is deviated from the center axis of the light tunnel for some length.
Conventionally, the light tunnel and the lamp are fixed at respective positions when the image projection apparatus is assembled. For example, the light tunnel is assembled at a given position in the image projection apparatus, and the lamp is fixed in the image projection apparatus by abutting a fixing reference face of the lamp to a member for fixing the lamp in the mage projection apparatus.
Therefore, if the processing precision of one or more parts to be fixed with the lamp is low, and the fixing position of the lamp deviates from the light axis of the lamp used as a desired position, the light axis of the lamp and the light guiding direction of the light tunnel deviate, with which efficient utilization of light beam becomes lower, and desired brightness cannot be secured for projection images. Further, if the light axis of the lamp and the light guiding position of the light tunnel deviate, the light emitted from the lamp may hit optical parts disposed around the light tunnel, with which the optical parts may be overheated and damaged.
In view of this issue, image projection apparatuses employing the optical lighting system using the light tunnel are disposed with an adjustment mechanism at an exit end of the light tunnel to adjust the position and rotation angle of the light tunnel to adjust a light focusing position onto the image generation element, in which the light can be guided to a desired lighting area on the image generation element.
However, even if the adjustment mechanism of the light tunnel is employed, it cannot confirm whether utilization of light beam is at a desired efficient level, which means even when the light guiding direction of the light tunnel is adjusted, it cannot guarantee the efficient utilization of light beam.
Therefore, if the desired brightness cannot be set for projection images after adjusting the position and rotation angle of the light tunnel, a re-adjustment work is required. The re-adjustment work can be performed by re-assembling the lamp with a consideration to the abutting part and re-fixed, but even if the re-adjustment work is performed, it cannot identify a deviation level of the light beam. Therefore, the re-adjustment work becomes a try-and-error operation, which is a complex work for users. Further, if the desired light intensity is not output from the image projection apparatus, it is determined that the reduction of light intensity occurs due to the wrong positioning of the light tunnel and the lamp, and this determination leads to replacement of the lamp and other related optical parts. However, the situation may not be improved just by replacing the lamp and other parts.